Dear AVI,
I think you r benifitted by my reply to Francis.
Moreover,in 3G We will replace BSCs by RNC and BTS by Node B.The work of MSC is distributed in MSC Server(control part)and Media Gateway(traffic or payload).
The remaining Core network remains to be same i mean to say HLR,EIR etc.We may have many ways to migrate from 2.5G to 3G.
By the way with whom you r working in INDIA
Muhammad Arshad